Possibly a compound of 身 ‎(mu, “body”) +‎ 霊 ‎(chi, “spirit, essence, soul”). Alternatively, may be an alteration of 睦 ‎(mutsu, “friendly, harmonious”, affix not used in isolation), probably caused by fusion with the Old Japanese emphatic nominal particle い ‎(i) in a manner similar to the alteration between kamu (combining form) and kami (standalone form) for 神 ‎(“god, spirit”), or kutsu (combining form) and kuchi (standalone form) for 口 ‎(“mouth”).